1. Field of the Invention
The present invention relates to an information transmission apparatus and an image reading apparatus, suitable for use in a facsimile machine, a copying machine, or the like, for transmitting information and reading information from an original without disturbance while preventing infrared radiation from being applied to a photodetector or a line sensor.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows a conventional image reading apparatus for use in a facsimile machine, a copying machine, or the like. As shown in FIG. 1, the conventional image reading apparatus has a feed mechanism 3 for moving an original 2 along an Y-axis indicated by the arrow Y, and light sources 4a, 4b such as fluorescent lamps, for example, energizable with high-frequency electric energy for applying light to the original 2 to scan and read information from an information-bearing surface of the original 2 along an X-axis perpendicular to the Y-axis. The image reading apparatus also includes a graded-index rod-lens array 6 to which light reflected by the information-bearing surface of the original 2 is applied, and a line sensor 8 comprising a linear array of CCDs for receiving the reflected light through the rod-lens array 6 and producing a readout signal representing the information of the original 2.
The conventional image reading apparatus shown in FIG. 1 operates as follows:
The original 2 is moved along the Y-axis by the feed mechanism 3. At the same time, the information-bearing surface of the original 2 is scanned along the X-axis by the light emitted from the light sources 4a, 4b. Light reflected by the information-bearing surface of the original 2 is applied through the rod-lens array 6 to the line sensor 8, which generates a readout signal representing the information of the original 2.
As the original 2 moves along the Y-axis, the line sensor 8 produces a readout signal per scanning line along X-axis in response to a readout drive signal from a driver circuit (not shown). In this manner, the original 2 is scanned along the Y- and X-axes so that the entire information-bearing surface thereof is two-dimensionally scanned and read.
The line sensor 8 of the conventional image reading apparatus is disadvantageous in that its sensitivity along the CCD array has a low uniformity level and its resolution is low.
FIG. 2 of the accompanying drawings illustrates spectral sensitivity characteristics of the line sensor 8, showing its relative sensitivity plotted against the wavelength of light applied thereto.
As shown in FIG. 2, the relative sensitivity of the line sensor 8 has a peak value in an infrared range where the applied light has a wavelength of 650 nm. Since the relative sensitivity of the line sensor 8 to the infrared range is higher than to a visible range of radiations, if some infrared radiation of light from the light sources 4a, 4b which comprise tungsten lamps or halogen lamps or extraneous light is added to the light that falls on the light sensor 8, then the line sensor 8 tends to operate in error. That is, the resolution of the line sensor 8 is liable to decrease, preventing the line sensor 8 to read the desired information with accuracy.